Theory of Operation
gear ratio for the front and rear pump gear train is
The front and rear hydraulic pumps (M) are variable
0.9487. The pump drive shafts (D) drive the cylinder
displacement, bent-axis, piston type pump. Two
blocks (G) through the pistons (F). The center shafts
identical pumps are used to generate oil flow in the
(E) is used to maintain alignment between the drive
hydraulic system. The pump can vary from minimum
shaft and cylinder block. The cylinder block is
displacement (K) to maximum displacement (L)
positioned at an angle to the drive shaft. As the
depending on hydraulic demand of the system.
cylinder block and drive shaft rotate, the pistons (F)
move in and out of their bores because of the angle.
A pump regulator (B) is attached to the top of pump
The pistons which are moving out of their bores draw
housing (C) for each pump. A pilot oil control signal to
oil from the hydraulic oil tank through the pump inlet
the regulator moves a piston which then directs pilot oil
port and then through ports in the valve plate (H). The
to the servo piston (I) which moves the valve plate (H)
pistons which are moving back into their bores push oil
and cylinder block (G) changing the pump
through ports in the valve plate out the front and rear
displacement. The feedback link (A), connected to the
discharge ports and to the control valve.
valve plate, also moves providing a mechanical
feedback to the remote control sleeve in the regulator.
The pump displacement, or flow rate, is varied by
The remote control sleeve blocks the flow of pilot oil to
changing the angle of the cylinder block with respect to
the servo piston and also traps the oil at both ends of
the drive shaft. Increasing the angle increases the
the servo piston stopping its movement.
distance that each piston travels into and out of the
bore which increases displacement. Decreasing the
Engine power is transferred to the pump drive shafts
angle reduces the distance that each piston travels
(D) by the dampener drive (flex coupling), the pump
into out of the bore which decreases displacement.
drive gearbox input drive shaft and a gear train. The